This proposal is for a three-year extension of a study investigating treatments for patients with comorbid alcohol dependence (AD) and posttraumatic stress disorder (PTSD). AD and PTSD are each associated with profound disruptions of functioning that are compounded in individuals with both disorders. Given the high rate of AD-PTSD comorbidity and the impairment associated with these disorders, it is imperative to identify effective treatments for these patients. The interrelation of AD and PTSD is complex with each disorder exacerbating the other, forming a vicious cycle. Recent years have seen advances in the treatment of each disorder, but no studies have examined the efficacy of treatments for patients presenting with both AD and PTSD. Treatment with naltrexone (NAL) plus counseling has been effective in treating AD, but its efficacy in AD patients with PTSD on AD and PTSD symptoms is unknown. Similarly, prolonged exposure (PE)therapy has proven effective in treating PTSD, but its efficacy in PTSD patients with AD on PTSD and AD symptoms is unknown. The hypothesized vicious cycle between AD and PTSD suggests that treatments targeting only one of the disorders will yield poorer outcomes in comorbid patients than treatment that addresses the two disorders concurrently. To date we have accrued 98 patients and we project entering a total of 105 patients into the study by the end of the current funding. Preliminary results with 70 patients are very promising. However, the projected sample of 105 patients does not afford sufficient power for reaching definitive conclusions about the relative efficacy of PE, AD and their combination. Accordingly, we are proposing to collect data from 75 additional patients with comorbid AD and PTSD to accrue a total of 180 patients into the study. This sample will provide adequate power to test our hypotheses. The study compares four treatment conditions in a 2 (NAL vs. placebo) by 2 (PE vs. no PE) design. The conditions are:1)100 mg. NAL plus PE; 2) NAL alone; 3) placebo plus PE; 4) placebo alone. A medication management intervention accompanies all treatment conditions. Symptoms will be evaluated before, during, and at the end of a 24-weeks treatment, and at 9 and 12 months following study entry. Our primary study's objective is to compare the short- and long-term effects of the combined treatments to those of each treatment in isolation on symptoms of AD and of PTSD. This research capitalizes on the unique expertise of two internationally renowned centers. One, the Treatment Research Center, known for expertise in pharmacotherapy for AD and the second, the Center for the Treatment and Study of Anxiety, known for cognitive behavioral treatment of PTSD. Therefore the findings from this study will be highly credible and should impact significantly on treatment recommendations for this impaired population.